Add a criterion benchmark

bench/Bench.hs

@@ -0,0 +1,29 @@
+import Criterion.Main
+import Language.Haskell.GhcMod.Target
+import TestUtils
+import Dir
+import System.IO.Temp
+import System.Process hiding (env)
+import Control.Monad
+
+main = defaultMain [
+    env setup $ \dir -> bgroup "simple-cabal" [
+        bench "nop" $ whnfIO (simpleCabalNop dir 1)
+      , bench "nop10" $ whnfIO (simpleCabalNop dir 10)
+      ]
+  ]
+
+setup = do
+  tdir <- createTempDirectory "/tmp" "ghc-mod-bench"
+  system $ "cp -rv \"bench/data/simple-cabal/\" \""++ tdir ++"\""
+
+  simpleCabalNop tdir 1 -- warmup dist/
+
+  return tdir
+
+simpleCabalNop :: FilePath -> Int -> IO ()
+simpleCabalNop dir n = withDirectory_ (dir </> "simple-cabal") $ do
+  _ <- runGhcModT defaultOptions $
+       forM_ [1..n] $ \_ -> do
+           runGmlT [Left "Main.hs"] (return ())
+  return ()